The purpose of this work is to determine the parameters of task-unrelated thought-intrusions both spontaneous (daydreams) and otherwise, as well as related mental activity such as insight, intuition, and mindwandering. An additional purpose is to investigate the relation between sustained attention and age. The purposes are accomplished through the use of controlled laboratory studies and retrospective questionnaires. Outcomes derived from these purposes and obtained over the fiscal year were: (a) Three samples of men and women tested in 1962-64 and 1980-84, who ranged in age from 20-92 years and who performed the Mackworth Clock Test, were observed to show no statistically significant age differences in number of spontaneous skin potential responses and a significant age effect for males for skin potential response latency revealing a U-shaped function with a minimum at middle-age; since both measures are taken as indicates of physiological arousal this outcome weakly suggests that middle-aged males are most highly aroused when performing a sustained attention task. (b) In an 18 year longitudinal study of the Mackworth Clock Test it was determined that only the change in target response time was significantly affected by the initial age of the men--hit likelihood, false alarms, skin potential latency, and number of spontaneous skin potential responses were unaffected--with young men becoming faster as they approached middle age and middle-aged men becoming slower as they aged; this outcome provides additional support for the notion resulting from cross-sectional studies that age has little effect on overall sustained attention. (c) In a Total Sample of 613 men and women the vigilance decrement in performance as indicated by likelihood of observing a target could be described precisely by a mathematical function comprised of two exponential terms, a negative exponential and an upper bounded term composed of the reciprocal of one plus a negative exponential, multiplied by constant; the simple negative exponential was interpreted as an effortful control process and the other component was interpreted as an automatic, nonconscious process.